Polypropylene resin compositions and interior automotive trim parts

ABSTRACT

A polypropylene resin composition is diclosed which comprises (a) 50-80% by weight of a specific polypropylene/ethylene-propylene copolymer composition, (b) 5-40% by weight of a specific ethylene/α-olefin copolymer rubber, (c) 1-10% by weight of a specific hydrogenated diene block copolymer, and (d) 10-30% by weight of talc, wherein the polypropylene component of the component (a) has a melt flow rate of 100-1,000 g/10 min and a C f  value (cross fractionation ratio) of not more than 0.5. The resin composition has excellent flowability and can impart excellent rigidity, high-temperature rigidity and impact resistance, and well-balanced combination thereof to the molded articles.

FIELD OF THE INVENTION

This invention relates to polypropylene resin compositions and moreparticularly, to the resin compositions havig a well-balancedcombination of flowability, rigidity, high-temperature rigidity andimpact resistance, which are suitable for the molding of interiorautomotive trim parts. The invention also relates to interior automotivetrim parts molded from said resin compositions.

BACKGROUND OF THE INVENTION

Polypropylene resins have been extensively used in automotiveapplications and in fields such as electrical appliances, miscellaneousgoods, films or the like, because the articles molded therefrom areexcellent in rigidity and high-temperature rigidity. The resincompositions for interior automotive trim parts have been required to beexcellent in not only rigidity and high-temperature rigidity, but alsoimpact resistance of molded articles and flowability of the resincompositions on molding. However, conventional polypropylene resins havebeen limited in the use range, since the articles molded therefrom aredeficient in impact resistance.

As typical polypropylene resins having improved impact resistance areknown propylene/ethylene block copolymers wherein propylene and ethyleneare block copolymerized and polypropylene resin compositions whereinpolypropylene is incorporated with an ethylene/α-olefin copolymerrubber. Such polypropylene resins have lower rigidity than a propylenehomopolymer. If those resins are incorporated with inorganic fillerssuch as talc, as the occasion demands, to make up for lowered rigidity,they are used mainly as molding materials for exterior automotive trimparts including automotive bumpers and interior automotive trim partsincluding instrument panels, console boxes, resin pillars and trims.However, the incorporation of inorganic fillers in a large amount isrequired to enhance the rigidity of the resin composition, which resultsin lowering the flowability of the resultant composition and also inincreasing the specific gravity of the resultant molded articles, withan increased weight of the products.

With a view to improving the impact resistance and stress-whiteningresistance of α-olefin polymers such as polypropylene and polyethyleneand α-olefin copolymers such as ethylene/propylene copolymer, variousresin compositions have been proposed wherein hydrogenated dienecopolymers are incorporated therein.

For example, JP-B-59-37294 discloses a resin composition wherein ahydrogenated 1,2-polybutadiene is incorporated in polymers or copolymersof α-olefin with 2 to 20 carbons, especially ethylene homopolyhmer,propylene homopolymer or ethylene/propylene copolymer. JP-B-62-45883 andJP-A-4-342752 disclose a resin composition wherein a hydrogenateddiblock copolymer of polybutadienes consisting of 1,2-block and1,4-block is incorporated in α-olefin polymers or copolymers, inparticular polypropylene.

JP-A-5-132606 discloses a resin composition wherein a hydrogenatedproduct of polybutadiene/conjugated diene block copolymers isincorporated in a crystalline propylene/ethylene block copolymer.JP-A-1-168743 and JP-A-1-168744 disclose a resin composition wherein ahydrogenated product of isoprene/butadiene copolymers is incorporated inpolyolefins.

The resin compositions are improved in both stress-whitening resistanceand impact resistance, but remarkably lowered in rigidity andhigh-temperature rigidity. Thus a practical use of such resincompositions is limited to the field of soft materials.

To enhance the reduced rigidity and high-temperature rigidity in theabove-described resin compositions wherein the hydrogenated diene blockcopolymers are incorporated in the propylene/ethylene block copolymers,it is created that the rigidity and high-temperature rigidity of themolded articles are improved with no increase in the specific gravity,by substitution for said propylene/ethylene block copolymers of highstereoregular polypropylenes disclosed in JP-A-62-187707. However, areduction in impact resistance of the molded articles is anticipated. Asmentioned above, the impact resistane of the polypropylene resincomositions is improved by the incorporation of the ethylene/α-olefincopolymer rubber and the hydrogenated polybutadiene polymer andcopolymer. However, the incorporation of these rubber components in alarge amount brings about new issue of lowering the rigidity andhigh-temperature rigidity of the molded articles as well as theflowability of the resin compositions. Thus, it has been desired todevelop a polypropylene resin composition being capable of improving theimpact resistance of the molded articles with no reduction in therigidity and high-temperature rigidity of the molded articles as well asthe flowability of the resin compositions.

Accordingly, an object of the present invention is to provide apolypropylene resin composition having a well-balanced combination ofthe flowability of the resin composition and the rigidity,high-temperature rigidity and impact resistance of the molded article,which is suitable as a molding material for interior automotive trimparts.

SUMMARY OF THE INVENTION

The above-mentioned object of the invention can be attained byincorporation of a specific hydrogenated diene block copolymer into acomposition comprising a specific high toughpolypropylene/ethylene-propylene copolymer composition, a specificethylene/α-olefin copolymer rubber and talc.

The present invention provides a polypropylene resin compositioncomprising

(a) 50-80% by weight of a polypropylene/ethylene-propylene copolymercomposition,

(b) 5-40% by weight of an ethylene/α-olefin copolymer rubber,

(c) 1-10% by weight of a hydrogenated diene block copolymer, and

(d) 10-30% by weight of talc,

each % by weight being based on the total weight of the resincomposition, wherein the polypropylene/ethylene-propylene copolymercomposition (a) has a melt flow rate of 10-300 g/10 min and comprises60-95% by weight of a polypropylene component and 5-40% by weight of anethylene/propylene copolymer component, the polypropylene component hasa melt flow rate of 100-1,000 g/10 min and a C_(f) value of not morethan 0.5 and the ethylene/propylene copolymer component has an ethylenecontent of 30-80% by weight; the ethylene/α-olefin copolymer rubber (b)is a copolymer of ethylene and an α-olefin of 4 or more carbons, has anethylene content of 25-90% by weight and contains a polyethylene crystalhaving a long period of 6-14 nm as determined by a small angle X-rayscattering; and the hydrogenated diene block copolymer (c) is a A--B orA--B--A block copolymer wherein a A segment is a 1,4-polybutadiene blockand a B segment is a 1,2-polybutadiene block, a polyisoprene block or abutadiene/isoprene copolymer block, and wherein not less than 85% of theunsaturated bonds are hydrogenated.

The present invention also provides an interior automotive trim partwhich is molded from the above resin composition having a melt flow rateof not less than 25 g/10 min and has the mechanical properties such as aflexural modulus at room temperature of not less than 2,400 Mpa, a heatdistortion temperature of not lower than 73° C. and an Izod impactstrength at room temperature of not less than 300 J/m.

DETAILED DESCRIPTION OF THE INVENTION

The polypropylene resin composition of the invention comprises:

(a) 50-80% by weight of a polypropylene/ethylene-propylene copolymercomposition,

(b) 5-40% by weight of an ethylene/α-olefin copolymer rubber,

(c) 1-10% by weight of a hydrogenated diene block copolymer, and

(d) 10-30% by weight of talc, and has a melt flow rate of not less than25 g/10 min, and further comprises

(e) a desired additive.

The molded articles from the above resin compositions satisfy variousproperties such as a flexural modulus at room temperature of not lessthan 2,400 Mpa, a heat distortion temperature of not lower than 73° C.(1820 kPa load) and an Izod impact strength at room temperature of notless than 300 J/m, required for interior automotive trim parts.

Each component constituting the polypropylene resin composition of thepresent invention is fully described below.

(a) Polypropylene/ethylene-propylene Copolymer Composition

The copolymer composition (a) is a principal component of the presentresin composition and comprises 60 to 95% by weight of the polypropylenecomponent and 40 to 5% by weight of the ethylene/propylene copolymercomponent.

The polypropylene component is a high stereoregular propylenehomopolymer which has a melt flow rate (MFRpp) of 100-1000 g/10 min,preferably 100-500 g/10 min as determined at 230° C. under a load of2.16 kg according to ASTM D 1238 and which has a narrow molecular weightdistribution wherein a cross fractionation ratio (C_(f) value) on thebasis of an elution temperature at 112° C. in the fractionation ofpolypropylene with o-dichlorobenzene is not more than 0.5. Thefractionation of polypropylene was carried out in accordance with themethod reported by J. B. P. Soares et al in "POLYMER" vol. 36, No. 8, pp1639-1654(1995). The cross fractionation ratio (C_(f) value) wasdetermined in the following manner. More specifically, a fractionationcolumn was prepared in which a stainless tube (15 cm length, 0.46 cmI/D) was packed with glass beads (each 0.1 mm diameter). 0.5 ml of asolution of polypropylene in o-dichlorobenzene at 140° C.(concentration: 2 mg/ml) was introduced into the fractionation columnkept at 140° C. The temperature of the fractionation column was cooleddown from 140° C. to 0° C. at the rate of 1° C./min to precipitatepolypropylene on the surface of glass beads. While maintaining thefractionation column at 0° C., o-dichlorobenzene at 0° C. wascontinuously introduced for 2 minutes into the fractionation column at arate of 1 ml/min, by which a polymer fraction soluble ino-dichlorobenzene was eluted and determined for the amount and molecularweight of the eluted polymer. This operation was repeated by gradientlyincreasing the elution temperatures by 10° C. intervals in the range of0-50° C., by 5° C. intervals in the range of 50-90° C. and by 3° C.intervals in the range of 90-140° C. Then, the amount of the polymereluted in each temperature, the weight fraction and molecular weight ofeach fraction were determined. From the determined results, there wereobtained an integrated value (C_(fl)) of the polymer fractions eluted atan elution temperature of less than 112° C. and an integrated value(C_(fh)) of the polymer fractions eluted at an elution temperature ofnot less than 112° C., and the cross fractionation ratio (C_(f)) wasexpressed as a ratio of C_(fl) to C_(fh) (C_(fl) /C_(fh)).

In the practice of the present invention, the C_(f) value was determinedby a cross fractionation device (CFC T-150A) manufactured by MitsubishiChemical Co. Ltd. using a column (SHODEX AD-806 M/S) manufactured byShowa Denko Co. Ltd. under the determining conditions as mentionedabove.

The melt flow rate (MFR_(pp)) of the polypropylene component has aneffect on the flowability of the resin composition and the toughness ofthe molded article. If it is too low, the melt flow characteristics ofthe resin composition lower, thus resulting in poor moldability. If itis too high, the toughness of the molded article lowers.

The C_(f) value is an index of a stereoregularity and molecular weightdistribution. Lower C_(f) value will provide higher stereoregularity andnarrower molecular weight distribution, which results in an increasedtoughness of the molded article.

The ethylene/propylene copolymer component is a random copolymer ofethylene and propylene and contains 30-80% by weight, preferably 35-55%by weight of an ethylene unit on the copolymer basis. The ethylenecontent in the copolymer component has an effect on the rigidity andimpact resistance of the molded article. If it is too high, the rigiditylowers. If it is too low, the impact resistance lowers.

The ethylene content is determined by the infrared spectrometry of theethylene/propylene copolymer using a culibration curve prepared from thestandard samples of ethylene/propylene copolymers produced with variedreaction ratios.

The polypropylene/ethylene-propylene copolymer composition (a) isadjusted to provide the melt flow rate (MFR_(a)) in the range of 10 to300 g/10 min, preferably 20 to 150 g/10 min. If MFR_(a) is too low, themoldability, i.e. flowability of the resin composition on injectionmolding to the molded article, e.g. interior automotive trim partsbecomes unsatisfactory. If it is too high, the impact resistance of themolded article lowers. The range of MFR_(a) to provide a well-balancedcombination of moldability and impact resistance is from 55 to 110 g/10min.

The composition ratio of the polypropylene component and theethylene/propylene copolymer component is varied depending on MFR_(pp)of the polypropylene component and the ethylene content of theethylene/propylene copolymer component, but 60 to 95% by weight of thepolypropylene component and 40 to 5% by weight of the ethylene/propylenecomponent.

In the resin composition of the present invention, the amount of thecopolymer composition (a) incorporated is 50 to 80% by weight,preferably 55 to 70% by weight on the basis of the resin composition.

The copolymer composition (a) is a component for imparting the rigidityand high-temperature rigidity to the molded article. If the amount ofthe component incorporated is too little, the rigidity andhigh-temperature rigidity of the molded article lower. If it is toomuch, the impact resistance of the molded article lowers.

The copolymer composition (a) may be prepared by any method if itsatisfies the above-mentioned requirements. It can be readily producedby a two-stage polymerization process wherein in the polymerization step(I) propylene is homopolymerized to produce a polypropylene having theabove-mentioned properties and in the polymerization step (II) ethyleneand propylene are copolymerized in the presence of the polypropyleneproduced in the polymerization step (I) to produce an ethylene/propylenecopolymer.

The homopolymerization of propylene and the copolymerization ofpropylene and ethylene may be conducted in a continous or batch process.In this case, there can be used a slurry polymerization carried out in ahydrocarbon solvent such as n-hexane, n-heptane, n-octane, benzene,toluene, a bulk polymerization carried out in a liquefied propylene anda gas phase polymerization. When the slurry polymerization is used inthe polymerization step (I), the polymerization is performed at atemperature of 20 to 90° C., preferably 50 to 80° C. and a pressure of 0to 5 MPa. For the gas phase polymerization, the polymerization isperformed at a temperature of 20 to 150° C. and a pressure of 0.2 to 5MPa. In the polymerization step (II), the polymerization is performed ata temperature of 20 to 80° C., preferably 40 to 70° C. and a pressure of0 to 5 MPa.

In the homopolymerization of propylene and the copolymerization ofethylene and propylene, hydrogen can be used to control the molecularweight. In the polymerization step (I), a hydrogen concentration iscontrolled to a higher level to prepare a polymer of high MFR_(pp). Inthe polymerization step (II), a hydrogen concentration is controlled toa very low level or a non-hydrogen state to prepare a copolymer of a lowMFR_(EP).

(b) Ethylene/α-olefin Copolymer Rubber

The ethylene/α-olefin copolymer rubber (b) has an ethylene content of 25to 90% by weight and is a copolymer rubber wherein ethylene and anα-olefin of 4 or more carbon atoms are copolymerized, which imparts theelasticity, especially elongation to the molded article.

The copolymer rubber also exhibits a long period in the range of 6 to 14nm, preferably 8 to 12 nm and its ethylene component is present as apolyethylene crystal, the long period being determined for the sheet bya small-angle X-ray scattering under the conditions: a radiation sourceCu--Kα ray; a step angle 0.02°; and a scanning range -4° to +4°, using aX-ray diffractometer (JEOL 8200T) manufactured by Japan Electron Co.Ltd.

The long period of the copolymer rubber (b) expresses thecrystallizability of polyethylene in the copolymer rubber. Thepolyethylene crystal in the copolymer rubber acts as a quasi crosslinkedsubstance to enhance the rubber. If the long period is too low, namelythe polyethylene crystal is too small or the crystallizability isinsufficient, the action as a quasi crosslinked substance becomesinsufficient. If the long period is too high, namely the polyethylenecrystal is too large, the copolymer rubber is easy to separate from thepolypropylene resin, which is responsible for reduction in tensileelongation of the article molded from the resin composition comprisingsuch copolymer rubber.

The ethylene/α-olefin copolymer rubbers are not limited in respect ofthe molecular weight, but it is preferable to use those having a meltindex (MI)(according to ASTM D 1238) of 0.1 to 30 g/10 min as determinedat 190° C. under a load of 2.16 kg. The ethylene content in theethylene/α-olefin copolymer rubber is preferably 45 to 90% by weight,more preferably 50 to 80% by weight.

Preferred ethylene/α-olefin copolymer rubber is a copolymer rubberwherein ethylene and an α-olefin of 4 or more carbons are copolymerized,for example a copolymer rubber constituted by two components such asethylene/1-butene copolymer rubber, ethylene/1-hexene copolymer rubber,ethylene/1-octene copolymer rubber or the like, a copolymer rubberconstituted by three components such as ethylene/1-butene/1-hexenecopolymer rubber or the like and a mixture thereof.

The amount of the ethylene/α-olefin copolymer rubber incorporated is 5to 40% by weight, preferably 10 to 30% by weight on the basis of theresin composition. The ethylene/α-olefin copolymer rubber has an effecton the impact resistance of the molded article. If the amount is toolittle, the improved effect of the impact resistance is unsatisfactory.If it is too much, the rigidity and high-temperature rigidity lower,possibly with impairing the flowability of the resin composition.

The ethylene/α-olefin copolymer rubber can be produced for example by apolymerization process as disclosed in JP-A-6-306121 wherein ethylene iscontinuously brought into contact with one or more substantially linearolefin polymers or α-olefins of 4-20 carbons under the polymerizationcondition in the presence of a catalyst composition comprising a 3-10group metal in the periodic table or a lanthanide metal, a metalcoordination complex and an activation co-catalyst.

(c) Hydrogenated Diene Block Copolymer

The hydrogenated diene block copolymer is a diene block copolymerwherein not less than 85%, preferably 90% or more of the unsaturatedbonds are hydrogenated. This diene block copolymer is a A--B or A--B--Ablock copolymer wherein the A segment is a 1,4-polybutadiene block andthe B segment is a 1,2-polybutadiene block, a polyisoprene block or abutadiene/isoprene copolymer block. The hydrogenated 1,4-polybutadieneblock constituting the A segment has a maximum melting temperature peakas determined by a differential scanning calorimeter in the range of 80to 120° C.

The hydrogenated diene block copolymer acts as a compatibilizing agentfor enhancing the compatibility between thepolypropylene/ethylene-propylene copolymer composition (a) and theethylene/α-olefin copolymer rubber (b), thereby to finely disperse thecopolymer rubber particles in the copolymer composition (a), thusimproving the impact resistance of the molded article.

The melting temperature of the hydrogenated 1,4-polybutadiene block isan index of the crystallizability. If the melting temperature is toolow, namely the crystallizability is low, the compatibility with theethylene/α-olefin copolymer rubber becomes unsatisfactory.

The hydrogenated 1,2-polybutadiene and/or polyisoprene blockconstituting the B segment of the hydrogenated diene block copolymer hasa compatibility with the copolymer composition (a).

The hydrogenated diene block copolymers can include, e.g. a hydrogenatedproduct of a diblock copolymer comprising a 1,4-polybutadiene and a1,2-polybutadiene, or the like, as disclosed in JP-B-62-45883; ahydrogenated product of a diblock or triblock copolymer comprising a1,4-polybutadiene and a 1,2-polybutadiene or a 1,4-polybutadiene and apolyisoprene, or the like, a hydrogenated product of a triblockcopolymer comprising a 1,4-polybutadiene, a 1,2-polybutadiene and apolystyrene, or a 1,4-polybutadiene, a 1,2-polyisoprene and apolystyrene, or the like, as disclosed in JP-A-4-342752; a hydrogenatedproduct of an isoprene/butadiene copolymer, or the like, as disclosed inJP-A-1-168743; and a hydrogenated product of anisoprene-butadiene//isoprene block copolymer, a hydrogenated product ofa butadiene-isoprene//butadiene block copolymer and a hydrogenatedproduct of an isoprene-butadiene block copolymer, or the like, asdisclosed in JP-A-1-168744. It is more preferable as a compatibilizingagent that the hydrogenated diene block copolymer is linear.

The amount of the hydrogenated diene block copolymer incorporated is 1to 10% by weight, preferably 2 to 5% by weight on the basis of the resincomposition. If the amount is too little, an effect of dispersing theethylene/α-olefin copolymer rubber (b) in the copolymer composition (a)as a compatibilizing agent becomes weak, so that a phase separation byheat on molding cannot be prevented. If it is too much, the resincomposition is plasticized and softened, thereby lowering the rigidityand high-temperature rigidity of the molded article.

(d) Talc

The talc is finely divided talc particles having an average particlesize of not more than 2 μm and in which the content of particles havinga size of 4 μm or more is not more than 4% by weight, and isincorporated as a component for imparting the rigidity to the moldedarticle. If the average particle size of the talc is too large and thecontent of particles having a size of 4 μm or more is too much, theimpact resistance, particularly surface impact resistance of the finalmolded article lowers. The particle size of the talc is measured byShimazu laser diffraction profile measuring device (SALD-2000)manufactured by Shimazu Manufacturing Co. Ltd., Japan.

The amount of the talc incorporated is 10 to 30% by weight, preferably15 to 25% by weight on the basis of the resin composition.

It is important that the amount of the talc incorporated is as arequired minimum level as possible, because talc gives adverse effectssuch as impairing the flowability of the resin composition, increasingthe specific gravity of the product, eventually increasing the productweight and producing a flow mark on the surface of the molded article.If the amount is too little, the rigidity and high-temperature rigidityof the molded article lower, thus making it difficult to maintain theflexural modulus and heat distortion temperature required as the basicproperties of interior automotive trim parts. If it is too much, thetensile elongation at break and impact resistance of the molded articletend to lower and a flow mark is easy to produce on the surface of themolded article.

(e) Other Components

If desired and necessary, various additives can be incorporated into theresin composition of the present invention, so long as the effects ofthe invention are not adversely influenced by such additives. Thoseadditives can include antioxidants, antistatic agents, colorants(pigments), nucleating agents, slip agents, release agents, flameretardants, ultraviolet absorbers, weathering agents, plasticizers andfree-radical generators.

The resin composition of the present invention comprises the components(a) to (d) in the respective prescribed amounts and if desired, anadditional component (e) in the prescribed amount.

The resin composition of the invention can be produced, for example, bythe following method. First, the predetermined amounts of the components(a) to (d) are mixed with a stabilizer and a colorant as an additive ofthe component (e) by means of a ribbon blender, tumbling mixer, Henschelmixer (trade name), supermixer or the like. The resulting mixture ismelt-kneaded with a roll mill, Banbury mixer, LaboPlastomill, single- ortwin-screw extruder or the like at a melt temperature of 150 to 300° C.,preferably 180 to 250° C. and then pelletized.

The resin composition of the invention can be subjected to theproduction of various moldings by any of various molding techniquesincluding injection molding, injection press molding, extrusion, vacuumforming and pressure forming. Of these molding techniques, injectionmolding and injection press molding are preferably used for producingmoldings from the composition.

The interior automotive trim parts of the present invention are thearticles molded into the desired shape from the resin compositionwherein the melt flow rate is controlled to not less than 25 g/10 min.These molded articles satisfy the basic performance required for theinterior automotive trim parts such as flexural modulus at roomtemperature (according to ASTM D 790) of 2400 MPa or more, heatdistortion temperature (1820 kPa load, according to ASTM D 648) of 73°C. or higher and Izod impact strength at room temperature (according toASTM D 256) of 300 J/m or more.

EXAMPLE

The invention is further illustrated by the following examples andcomparative examples.

1) Components of Resin Composition

(a) Component

a-1) Polypropylene/ethylene-propylene Copolymer Composition

Polypropylene component

    ______________________________________                                        MFR.sub.pp          200 g/10 min                                                Cf value 0.31                                                                 Proportion 90% by weight                                                    ______________________________________                                    

Ethylene/propylene copolymer component

    ______________________________________                                        MFR.sub.EP          0.0001 g/10 min                                             Ethylene content 40% by weight                                                Proportion 10% by weight                                                    ______________________________________                                    

Copolymer composition

    ______________________________________                                               MFR.sub.a    48 g/10 min                                               ______________________________________                                    

a-2) Polypropylene/ethylene-propylene Copolymer (for comparison)

Polypropylene component

    ______________________________________                                        MFR.sub.pp          200 g/10 min                                                Cf value 0.60                                                                 Proportion 90% by weight                                                    ______________________________________                                    

Ethylene-propylene copolymer component

    ______________________________________                                        MFR.sub.EP          0.00008 g/10 min                                            Ethylene content 45% by weight                                                Proportion 10% by weight                                                    ______________________________________                                    

Copolymer composition

    ______________________________________                                               MFR.sub.a    46 g/10 min                                               ______________________________________                                    

(b) Ethylene/α-Olefin Copolymer Rubber

b-1) Ethylene/1-octene Copolymer Rubber

    ______________________________________                                        Ethylene content    76.3% by weight                                             MI 1.1 g/10 min                                                               Long period 8.6 nm                                                          ______________________________________                                    

b-2) Ethylene/1-octene Copolymer Rubber

    ______________________________________                                        Ethylene content    76.2% by weight                                             MI 4.3 g/10 min                                                               Long period 9.2 nm                                                          ______________________________________                                    

b-3) Ethylene/1-octene Copolymer Rubber

    ______________________________________                                        Ethylene content    77.9% by weight                                             MI 2.9 g/10 min                                                               Long period 9.3 nm                                                          ______________________________________                                    

b-4) Ethylene/1-butene Copolymer Rubber

    ______________________________________                                        Ethylene content    90% by weight                                               MI 2.1 g/10 min                                                               Long period 11.2 nm                                                         ______________________________________                                    

b-5) Ethylene/1-butene Copolymer Rubber

    ______________________________________                                        Ethylene content    80% by weight                                               MI 3.0 g/10 min                                                               Long period 10.2 nm                                                         ______________________________________                                    

b-6) Ethylene/1-butene Copolymer Rubber

    ______________________________________                                        Ethylene content    85% by weight                                               MI 3.6 g/10 min                                                               Long period 10.9 nm                                                         ______________________________________                                    

b-7) Ethylene/1-hexene Copolymer Rubber

    ______________________________________                                        Ethylene content    85% by weight                                               MI 1.3 g/10 min                                                               Long period 11.0 nm                                                         ______________________________________                                    

b-8) Ethylene/1-hexene/1-butene Copolymer Rubber

    ______________________________________                                        Ethylene content    85% by weight                                               Hexene content 14% by weight                                                  MI 3.5 g/10 min                                                               Long period 10.8 nm                                                         ______________________________________                                    

b-9) Ethylene/propylene Copolymer Rubber (for comparison)

    ______________________________________                                        Ethylene content       78% by weight                                            MI 0.4 g/10 min                                                               Long period 15.6 nm                                                           Mooney viscosity MLI + 4 (100° C.) 60                                ______________________________________                                    

(c) Hydrogenated Diene Block Copolymer

c-1)Hydrogenated(1,4-polybutadiene//1,2-polybutadiene/1,4-polybutadiene//1,4-polybutadiene)blockCopolymer

    ______________________________________                                        Structure             A-B-A type                                                % Hydrogenation 95%                                                           MFR (230° C., 2.16 kg load) 1.4 g/10 min                               Total A segment 30% by weight                                                 Melting temperature 97° C.                                             B segment 70% by weight                                                     ______________________________________                                    

c-2)Hydrogenated(1,4-polybutadiene//1,2-polybutadiene/1,4-polybutadiene//1,4-polybutadiene)blockCopolymer

    ______________________________________                                        Structure             A-B-A type                                                % Hydrogenation 95%                                                           MFR (230° C., 2.16 kg load) 0.4 g/10 min                               Total A segment 30% by weight                                                 Melting temperature 92° C.                                             B segment 70% by weight                                                     ______________________________________                                    

c-3) Hydrogenated(1,4-polybutadiene//1,4-polybutadiene/polyisoprene)block Copolymer

    ______________________________________                                        Structure             A-B type                                                  % Hydrogenation 95%                                                           MFR (230° C., 2.16 kg load) 14 g/10 min                                Total A segment 30% by weight                                                 Melting temperature 92° C.                                             B segment 70% by weight                                                     ______________________________________                                    

(d) Talc

d-1) Finely Divided Talc Particles

    ______________________________________                                        Average particle size 1.3 μm                                                 Content of particles having 2.5% by weight                                    a size of 4 μm or more                                                   ______________________________________                                    

2) Method for the Measurement of Physical Properties

The physical properties of each component were measured by the followingmethods.

(a) Long Period of Ethylene/α-Olefin Copolymer Rubber

The pellets of the ethylene/α-olefin copolymer rubber were melt at 230°C. under 10 MPa for 5 minutes and cooled to 50° C. under 10 MPa toprepare a sheet having a thickness of 500 μm. The long period of thesheet was measured by a small-angle X-ray scattering using a X-raydiffractometer (JEOL 8200 T) manufactured by Japan Electron Co. Ltd.under the following conditions: radiation ray Cu--Kα ray; step angle0.02°; scanning range -4° to +4°.

(b) Melting Temperature of A Segment in the Hydrogenated Diene BlockCopolymer

10 mg of a sample was introduced into a differential scanningcalorimeter (1090 type DSC) manufactured by E. I. du Pont de Nemours &Co. First, the sample was heated to 230° C. at a rising rate of 30°C./min and kept at 230° C. for 10 minutes. Then, the sample was cooledto -60° C. at a decreasing rate of 20° C./min and kept at -60° C. for 10minutes. The melting temperature was read from a peak of a thermogramobtained when the sample was again elevated at a rising rate of 20°C./min.

(c) Melt Flow Rate of Each Component

The pellets of the component to be measured were determined under theconditions of 230° C. and a load of 2.16 kg according to ASTM D 1238.

(d) Melt Index (MI) of Ethylene/α-Olefin Copolymer Rubber

The pellets of the ethylene/α-olefin copolymer rubber were determinedunder the conditions of 190° C. and a load of 2.16 kg according to ASTMD 1238.

3) Preparation of Resin Composition

Examples 1-10 and Comparative Examples 1-8

Each of the above-mentioned components was mixed in the respectiveproportions shown in Tables 1 and 2. The mixture was incorporated with aphenolic antioxidant as a stabilizer: 0.05 part by weight oftetrakis[methylene-3-(3,5-di-tert.butyl-4-hydroxyphenyl)propionate]methane,a phosphorus antioxidant: 0.05 part by weight oftetrakis(2,4-di-tert.butyl phenyl)-4,4-biphenylene-diphosphonite, aneutralizer: 0.1 part by weight of calcium stearate and a dispersant:0.2 part by weight of zinc stearate. The resulting mixture was stirredand mixed with a Henschel mixer (trade name) for 3 minutes, melt-kneadedat 200° C. with a twin-screw extruder (PCM-45) manufactured by IkegaiTekko Co., Ltd., Japan and pelletized to prepare the resin compositionsof Examples 1-10 and Comparative Examples 1-8.

                                      TABLE 1                                     __________________________________________________________________________                              Example No.                                                                   1  2  3  4  5  6  7  8  9  10                       __________________________________________________________________________    Composition                                                                     (a) Polypropylene/ethylene-propylene copolymer composition                    Component No. a-1 a-1 a-1 a-1 a-1 a-1 a-1 a-1 a-1 a-1                         Proportion (wt %) 64 62 65 60 61 60 60 60 62 65                               (b) Ethylene/α-olefin copolymer rubber                                  Component No. b-1 b-1 b-3 b-4 b-5 b-6 b-8 b-4 b-1 b-3                         Proportion (wt %) 13 6.5 12 17 7.5 17 17 17 6.5 12                            Component No.  b-2   b-7    b-2                                               Proportion (wt %)  6.5   7.5    6.5                                           (c) Hydrogenated diene block copolymer                                        Component No. c-1 c-1 c-1 c-1 c-1 c-1 c-1 c-2 c-3 c-3                         Proportion (wt %) 3 5 3 3 4 3 3 3 5 3                                         (d) Finely divided talc particles (wt %) 20 20 20 20 20 20 20 20 20 20                                                            Physical Properties       (1) Melt flow rate (g/10 min) 33 34 30 29 29 33 30 29 30 31                   (2) Flexural modulus (MPa) 2510 2580 2530 2500 2480 2460 2470 2500 2470                                                          2475                       (3) Heat distortion temperature (° C.) 74 73 76 76 74 75 75 77                                                            73 73                      (4) Tensile elongation at break (%) >500 >500 >500 >500 >500 >500 >500                                                           >500 >500 >500                                                                 (5) Izod impact                                                              strength (J/m) 310                                                            320 420 480 320 390                                                           400 400 310 400          __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________                              Comparative Example No.                                                       1  2  3  4  5  6  7  8                              __________________________________________________________________________    Composition                                                                     (a) Polypropylene/ethylene-propylene copolymer composition                    Component No. a-1 a-1 a-1 a-1 a-1 a-1 a-2 a-1                                 Proportion (wt %) 64 62 65 62 62 44 65 63                                     (b) Ethylene/α-olefin copolymer rubber                                  Component No. b-1 b-1 b-3   b-2 b-2                                           Proportion (wt %) 16 9 15   18 12                                             Component No.  b-2                                                            Proportion (wt %)  9                                                          (c) Hydrogenated diene block copolymer                                        Component No.    c-1 c-3 c-1 c-1 c-1                                          Proportion (wt %)    18 18 3 3 3                                              (d) Finely divided talc particles (wt %) 20 20 20 20 20 35 20 20                                                            Physical Properties                                                           (1) Melt flow rate (g/10                                                     min) 32 32 33 22 29 23 25                                                     30                               (2) Flexural modulus (MPa) 2520 2500 2560 1700 1600 3300 3000 2400                                                          (3) Heat distortion                                                          temperature (° C.)                                                     74 73 76 58 57 75 82 73                                                        (4) Tensile elongation at                                                    break (%) 160 150 180 >500                                                    >500 30 100 80                   (5) Izod impact strength (J/m) 130 120 170 580 600 40 150 180               __________________________________________________________________________

4) Molding of Resin Composition

The pellets of each composition obtained in Examples 1-10 andComparative Examples 1-8 were determined for MFR according to the methodas mentioned above. From those pellets, test pieces having the givendimensions were molded by injection molding at a molding temperature of210° C. and a mold temperature of 40° C., and then subjected to theevaluation tests. The results were shown in Tables 1 and 2.

5) Evaluation Test

(a) Flexural Modulus (Three-point Flexural Modulus)

Test pieces having a length of 130 mm, a width of 13 mm and a thicknessof 6.4 mm were used and measured for flexural modulus under thecondition of 23° C. according to ASTM D 790 to evaluate the rigidity.

(b) Heat Distortion Temperature (° C.)

Test pieces having a length of 130 mm, a width of 13 mm and a thicknessof 6.4 mm were used and measured for heat distortion temperature underthe condition of 1820 kPa load according to ASTM D 648 to evaluate thehigh-temperature rigidity.

(c) Tensile Tests (MPa, %)

Test pieces having a length of 246 mm, a width of 19 mm and a thicknessof 3.2 mm were used and measured for tensile strength at yield point andtensile elongation at break under the condition of 23° C. according toASTM D 638.

(d) Izod Impact Strength (J/m)

Test pieces having a length of 63.5 mm, a width of 12.7 mm and athickness of 6.4 mm were notched and measured for Izod impact strengthat 23° C. according to ASTM D 256 to evaluate the impact resistance.

6) Evaluation Results

As apparent from Examples 1 to 8 shown in Table 1, the resincompositions of the present invention have excellent flowability and thearticles molded from such resin compositions have excellent rigidity andimpact resistance. These properties include MFR of 25 g/10 min or morefor the resin compositions and flexural modulus at room temperature of2400 MPa or more, heat distortion temperature of 73° C. or higher andIzot impact strength at room temperature of 300 J/m or more for themolded articles, satisfying the basic characteristics required forinterior automotive trim parts.

In contrast, the resin compositions of Comparative Examples 1 to 3 notcontaining the hydrogenated diene block copolymer have a poor balancebetween the rigidity and impact resistance, especially poor impactresistance, and also have a reduced tensile elongation at break. Theresin compositions of Comparative Examples 4 and 5 containing more than10% by weight of the hydrogenated diene block copolymer exhibit animproved impact resistance, but remarkably low rigidity andhigh-temperature rigidity.

The resin composition of Comparative Example 6 containing more than 30%by weight of talc demonstrates a lowered flowability and a loweredtensile elongation at break due to an addition of talc in a largequantity.

The resin composition of Comparative Example 7 wherein conventionalpropylene block copolymer (a-2) was incorporated in place of thepolypropylene/ethylene-propylene copolymer composition (a-1) exhibits aremarkably low toughness in terms of impact resistance and tensileelongation at break.

The resin composition of Comparative Example 8 using theethylene/α-olefin copolymer rubber having the long period of 14 nm ormore exhibits a remarkably low impact resistance and tensile elongationat break.

EFFECT OF THE INVENTION

By incorporating a specific amount of talc into a resin componentcomprising a specific high tough polypropylene/ethylene-propylenecopolymer composition, a specific ethylene/α-olefin copolymer rubber anda specific hydrogenated diene block copolymer, the polypropylene resincompositions of the present invention exhibit excellent flowability, andalso the articles molded therefrom are superior in high-temperaturerigidity and impact resistance to those molded from conventionalpolypropylene resin compositions. Accordingly, the use of the presentresin compositions as a molding material can make interior automotivetrim parts large-sized, thin-walled, light-weight and low cost.

What is claimed is:
 1. A polypropylene resin composition comprising(a)50-80% by weight of a mixture of polypropylene and an ethylene-propylenecopolymer, (b) 5-40% by weight of an ethylene/α-olefin copolymer rubber,(c) 1-10% by weight of a hydrogenated diene block copolymer, and (d)10-30% by weight of talc,each % by weight being based on the totalweight of the resin composition, wherein the mixture of polypropyleneand ethylene-propylene copolymer (a) has a melt flow rate of 10-300 g/10min under the conditions of a temperature of 230° C. and a load of 2.16kg and comprises 60-95% by weight of a polypropylene component and 5-40%by weight of an ethylene/propylene copolymer component, thepolypropylene component has a melt flow rate of 100-1,000 g/10 min underthe conditions of a temperature of 230° C. and a load of 2.16 kg and aC_(f) value of not more than 0.5 and the ethylene-propylene copolymercomponent has an ethylene content of 30-80% by weight; theethylene/α-olefin copolymer rubber (b) is a copolymer of ethylene and anα-olefin of 4 or more carbons, has an ethylene content of 25-90% byweight and contains a polyethylene crystal having a long period of 6-14nm as determined by a small angle X-ray scattering; and the hydrogenateddiene block copolymer (c) is a A--B or A--B--A block copolymer wherein aA segment is 1,4-polybutadiene block and a B segment is a1,2-polybutadiene block, a polyisoprene block or a butadiene/isoprenecopolymer block, and wherein not less than 85% of the unsaturated bondsare hydrogenated.
 2. The resin composition of claim 1 wherein theethylene/α-olefin copolymer rubber has a long period of 8-12 nm asdetermined by a small angle X-ray scattering.
 3. The resin compositionof claim 1 wherein the ethylene/α-olefin copolymer rubber is a copolymerrubber constituted by two components, selected from the group consistingof ethylene/1-butene copolymer rubber, ehtylene/1-hexene copolymerrubber and ethylene/1-octene copolymer rubber, a copolymer rubberconstituted by three components comprising ethylene, 1-butene, and1-hexene or a mixture thereof.
 4. The resin composition of claim 1wherein the hydrogenated 1,4-polybutadiene block constituting thehydrogenated diene block copolymer has a melting temperature of 80 to120° C. as determined by a differential scanning calorimeter.
 5. Theresin composition of claim 1 wherein talc is finely divided talcparticles having an average particle size of not more than 2 μm and thecontent of the particles of not less than 4 μm is not more than 4% byweight.
 6. The resin composition of claim 1 further comprising a desiredadditive.
 7. The resin composition of claim 6 wherein the additives areantioxidants, antistatic agents, colorants (pigments), nucleatingagents, slip agents, release agents, flame retardants, ultravioletabsorbers, weathering agents, plasticizers and free-radical generators.8. An interior automotive trim part which is molded from the resincomposition of claim 1 having a melt flow rate of not less than 25 g/10min and which has a flexural modulus at room temperature of not lessthan 2,400 Mpa, a heat distortion temperature of not lower than 73° C.and an Izod impact strength at room temperature of not less than 300J/m.